In recent years, it has been pointed out that toxic gas having harmful influence on a human body is discharged from various new building materials employed in dwelling houses and so forth. Formaldehyde gas has been listed as one of such toxic gases. Therefore, demand for collection of the formaldehyde gas in the ambient air and analysis of formaldehyde concentration is becoming greater.
The basic principle of the analysis of formaldehyde concentration well known in the art is as follows. Formaldehyde (HCHO) and AHMT (4-amino-3-hydrazino-5-mercapto-1,2,4-triazole) react under alkaline condition to form a product which indicates a red color when oxidized by KIO.sub.4 (potassium periodate). The density of this color development is in proportion to the concentration of the formaldehyde. Therefore, an analytical curve for performing the analysis of the unknown sample is prepared with respect to the relation between light transmittance (absorbance) in the vicinity of wavelength 550 nm and concentration of formaldehyde. The standard operating procedure is as follows.
1 A given amount of the sample solution into which the formaldehyde is admixed, is measured by means of a pipette and filled into a glass vessel. PA0 2 A given amount of alkaline reagent is measured by means of a pipette and added to the glass vessel. PA0 3 A given amount of AHMT reagent is measured by means of a pipette and added to the glass vessel, and left for about 20 minutes while mixing. PA0 4 A given amount of KIO.sub.4 reagent is measured by means of the pipette and added to the glass vessel. PA0 5 After transferring to a color comparison tube, the color development density of the resultant solution is measured by means of a colorimeter or a spectrophotometer. PA0 6 The operations of 1 to 5 are performed by using standard solutions (a few of which have different concentrations) containing a known amount of formaldehyde, respectively to prepare an analytical curve. PA0 7 The formaldehyde concentration contained in the sample solution is derived by comparison with the analytical curve.
In addition, the formaldehyde concentration in the ambient air can be converted by the following equation, EQU Cv=Cl.times.(A.times.22.4)/(B.times.M.times.Q)
wherein,
Cv: HCHO concentration in the ambient air (ppm) PA1 Cl: HCHO content contained in an aliquot portion of liquid (.mu.g) PA1 A: Collecting liquid amount (ml). PA1 B: Amount of the aliquot portion of liquid (ml) PA1 M: Molecular weight of HCHO PA1 Q: Air suction amount (l) PA1 passing a given amount of air to be inspected through a collecting vessel filled with a given amount of 2N--KOH solution; PA1 filling a given amount of AHMT reagent into the collecting vessel and leaving the reagent for a given amount of time; PA1 setting a standard color solution to an absorptiometer for adjusting the indication value thereof to a predetermined value; and PA1 adding a given amount of KIO.sub.4 reagent to the collecting vessel, setting the collecting vessel to the absorptiometer, and detecting formaldehyde concentration from the indication value of the absorptiometer. PA1 passing a given amount of air to be inspected through a collecting vessel filled with a given amount of 2N--NaOH solution; PA1 filling a given amount of AHMT reagent prepared by using HClO.sub.4 into the collecting vessel and leaving the reagent for a given amount of time; PA1 setting a standard color solution to an absorptiometer for adjusting the indication value thereof to a predetermined value; and PA1 adding a given amount of KIO.sub.4 reagent to the collecting vessel, setting the collecting vessel to the absorptiometer, and detecting formaldehyde concentration from the indication value of the absorptiometer. PA1 passing a given amount of air to be inspected through a collecting vessel filled with collecting liquid prepared by adding a given amount of AHMT solution to a given amount of 2N--KOH solution, or with a collecting liquid prepared by adding a given amount of AHMT solution prepared by using HClO.sub.4 solution to a given amount of 2N--NaOH solution; PA1 setting a standard color solution to an absorptiometer for adjusting the indication value thereof to a predetermined value; and PA1 setting the collecting vessel to the absorptiometer, and detecting formaldehyde concentration from the indication value of the absorptiometer.
However, according to the conventional method for analyzing formaldehyde set forth above, since the analyzing operation becomes extremely complicated, it is necessary to take the formaldehyde collected in the building site back to a location where an analyzing equipment is organized and implement the analysis of concentration. Therefore, the result of the analysis cannot be obtained at the site where the gas is collected, causing the possibility of delay in judgement and assessment. Meanwhile, the condition of the sample may also be changed by transportation of the collected sample, by transferring of vessels, and during storage until analysis implementation, all of which may create a situation in which accurate data cannot be obtained.
Furthermore, since a knowledge in chemistry is required for the calculation of the concentration, and since close attention becomes necessary upon handling the chemicals for analysis, analysis cannot be implemented except by a skilled person in chemical analysis. By this, problems such as long-time requirement and high cost by relying on an analyzing organization or the like are apt to arise.